Robust Design: Reducing Variation and its Impact Design Production Measurement Reliability

Thomas J. Howard Head of Robust Design Group

2014 CT Scanning , Munich – Robust Design 2 DTU Mechanical Engineering

Exemplifying Robust Design Functional Performance: Chair must not rock more than 2 mm

Design Parameters: 1. Length of legs 2. Angle of legs 3. Flatness of seat 4. Flatness of

ground 5. …

Design Parameters: ?

∝ Functional Variance

Design Sensitivity

Parameter Variance 𝐱𝐱

2014 CT Scanning , Munich – Robust Design 3 DTU Mechanical Engineering

Six Theta® Robust Design

2014 CT Scanning , Munich – Robust Design 4 DTU Mechanical Engineering

Six Theta® Robust Design: Design Clarity Parts have intended constraining surfaces, but too many potential and unnecessary constraining surfaces lead to a lack of predictability in terms of how the part will actually function. The intended and actual number of constraining surfaces can be visualised in a cockpit, thereby providing an overview of the current state of sensitivity in the design. Impact of ambiguous interfaces: • Variation in performance • Unclear tolerance chains • Unclear load transmission

2014 CT Scanning , Munich – Robust Design 5 DTU Mechanical Engineering

Six Theta® Robust Design Methods

Issues faced

Unpredictable wear and life of turbines, costly and frequent maintenance

Posible quality issues damaging premium brand image, missing launch dates Long rampup times, delayed launches and low yields due to safety critical product

Kinematic design

Design Clarity

Six Theta methods

Six Theta KPIs

Lagging Indicators

Axiomatic Design

Tolerance Design Production

Yield Customer

Complaints Service

Requests Defect ID

Parameter Sensitivity

Monte Carlo

Planning Concept Design

System Design

Detail Design Testing Ramp

Up Use Maintenance Disposal

2014 CT Scanning , Munich – Robust Design 6 DTU Mechanical Engineering

Six Theta® Robust Design Indicators

Planning Concept Design

System Design

Detail Design Testing Ramp

Up Use Maintenance Disposal Issues faced

Kinematic design

Design Clarity

Unpredictable wear and life of turbines, costly and frequent maintenance

Posible quality issues damaging premium brand image, missing launch dates Long rampup times, delayed launches and low yields due to safety critical product

Parameter Sensitivity

Axiomatic Design

Tolerance Design

Predicta-bility Index

Theta Value

Mobility

Coupling Degree

Tolerance Index

ProductionYield

Customer Complaints

Service Requests

Defect ID

Monte Carlo Yield Estimate

Six Theta methods

Six Theta KPIs

Lagging Indicators

2014 CT Scanning , Munich – Robust Design 7 DTU Mechanical Engineering

In general Robust Design focusses on the Design phase removing reliability issues before production or

measurement. However, some nasties sneak through from time to time, where CT scanning could assist.

2014 CT Scanning , Munich – Robust Design 8 DTU Mechanical Engineering

GM Ignition Switch Recall

• fine of $35 million

• recall of 2.6 million vehicles

• death of at least 13 people.

8

Ignition Swtich Mode of Action

9

START

OFF

ACC

ON

towards START

Rotational movement of switch plate

Locking switch positions The position of modes “ON” (or Run) and “Accessory” are defined by notches in the switch plate. A plunger, forced by a spring, extends into the notches, intending to hold the mechnism stable until the key is turned.

Slipping/Bouncing

2014 CT Scanning , Munich – Robust Design 10 DTU Mechanical Engineering

McSwain Engineering CT Scans

2014 CT Scanning , Munich – Robust Design 11 DTU Mechanical Engineering

McSwain Engineering CT Scans

Failed Product (2005) New Version (2008)

2014 CT Scanning , Munich – Robust Design 12 DTU Mechanical Engineering

2005 – 3.68mm

McSwain Engineering images

2014 CT Scanning , Munich – Robust Design 13 DTU Mechanical Engineering

2006 – 3.71mm

McSwain Engineering images

2014 CT Scanning , Munich – Robust Design 14 DTU Mechanical Engineering

2007 – 3.95mm

McSwain Engineering images

2014 CT Scanning , Munich – Robust Design 15 DTU Mechanical Engineering

2007 – 4.77mm

McSwain Engineering images

2014 CT Scanning , Munich – Robust Design 16 DTU Mechanical Engineering

2008 – 5.08mm

McSwain Engineering images

2014 CT Scanning , Munich – Robust Design 17 DTU Mechanical Engineering

The new chevy – 8.00mm

McSwain Engineering images

2014 CT Scanning , Munich – Robust Design 18 DTU Mechanical Engineering

McSwain Engineering images

2014 CT Scanning , Munich – Robust Design 19 DTU Mechanical Engineering

Minimal constraints theory!!

2014 CT Scanning , Munich – Robust Design 20 DTU Mechanical Engineering

LONG contact surfaces

2014 CT Scanning , Munich – Robust Design 21 DTU Mechanical Engineering

15,7

15,8

15,9

16,0

16,1

16,2

16,3

16,4

16,5

16,6

16,7

1 2 3 4 5 6 7 8 9 10 11

38,18

38,22

38,26

38,30

38,34

38,38

38,42

1 2 3 4 5 6 7 8 9 10 11

Specified nominal values Measured variation of example ignition switches

h1=16,3 mm

Dimensions of components

Dimensions of assembled device

h2=38,2 mm

Source: Eifler T., Olesen J.L. and Howard T.J.: Robustness and Reliability of the GM Ignition Switch - A forensic Engineering case. In: Howard T.J. and Eifler T.: Proceedings of the International Symposium on Robust Design - ISoRD14. Copenhagen, Denmark.

Switch number

Switch number

Hei

gh

t h

2 [m

m]

Nominal value

Nominal value

Hei

gh

t h

1 [m

m]

2014 CT Scanning , Munich – Robust Design 22 DTU Mechanical Engineering

CT Image by DTI

2014 CT Scanning , Munich – Robust Design 23 DTU Mechanical Engineering

CT Image by DTI

2014 CT Scanning , Munich – Robust Design 24 DTU Mechanical Engineering

McSwain Engineering CT Scans

McSwain Engineering images

2014 CT Scanning , Munich – Robust Design 25 DTU Mechanical Engineering

CT Scanning as a great tool for Forensic Engineering to uncover sources of variation…

…when the product is not robust enough!

GMσD Global Manufacturing Variatiσn Database

Horizon 2020 application

Factories of the Future (FoF-14-2015)

Topic: Integrated design and management of production machinery and processes

Deadline: Feb 2015

Duration: 4years

2014 CT Scanning , Munich – Robust Design 27 DTU Mechanical Engineering

Challenges in Industrial Practice

Current practices rely on subjective jugement

or pilot production

2014 CT Scanning , Munich – Robust Design 28 DTU Mechanical Engineering

Aim – Design to Process Capabilities (DtPC)

Conceptual Design

Pilot Production

Ramp Up / Production

Measurement reports

Evaluation of Production capabilities

MσD

Detail Design Tolerance Activities

2014 CT Scanning , Munich – Robust Design 29 DTU Mechanical Engineering

PMσD Structure (Local Manufacturing Variation Database)

Manufacturing

Prod

uct d

evel

opm

ent

Assembly

Planning

Concept Design

System Design

Detail Design

PMσD

Measurement reports

Design Guidelines/ Interface/CAD plugin

PMσD: Benefits & Challenges for the generalisation of data

feature-based variation data with reference to GD&T annotation

Interaction effects – Influence of product characteristics

Interaction effects – Influence of machinery design

Alignment of measurement procedures and (advanced) technologies

…

2014 CT Scanning , Munich – Robust Design 30 DTU Mechanical Engineering

…

Shee

t met

al fo

rmin

g mandrel

roller tool

blank

GMσD Structure (Global Manufacturing Variation Database)

Inje

ctio

n m

ould

ing

Anonomysed variation data

GMσD

Design Interface

Quantifying manufacturing capabilities across processes and industries, leading to a new standard for tolerance allocation.

2014 CT Scanning , Munich – Robust Design 31 DTU Mechanical Engineering

Questions?

Thomas J. Howard

Head or Robust Design Group

Email: thow@mek.dtu.dk

Tel: 0045 45 25 47 41

Skype: thomas-james-howard